The study of how animals and man collect vapor and move it to the operational part of their olfactory systems (the olfactory epithelium) is a developing area of inquiry. A project conducted in the Auburn Institute of Biological Detection Lab involved training dogs to wear a thermocouple placed at the entrance to one nostril so that the changes in the velocity of the inspired and expired air could be used to measure individual sniffs. The dogs were then tested with different types of odors under different conditions to develop information about airflow patterns in the nose while sniffing. This research indicated that a baseline period of respiration followed by a bout of high rate sniffing, which ceases when the odor is removed.
Flow visualization has been used to observe canine olfactory airflows. Two general types of such flows have been observed: high-frequency (“short”) sniffing during close inspection of an object and low-frequency (“long”) sniffing of more distant objects. In both cases the inspiratory airflow pattern is essentially an inviscid sink flow. However, a comparison of the two types of olfaction shows that the dog has some directional control over the twin turbulent jets generated from its nostrils during expiration. During close inspection of a scent source from directly above, the canine nostrils direct the expired air rearward, so that it does not impinge upon the object. However, when “scanning” the vicinity of a scent source on the ground, the motion of the dog's nose can aim its expiratory jets directly at the source. If particulates are present, they are then readily entrained and can be subsequently inspired. No significant distinction was observed between pet animals and a trained explosive detection dog regarding this behavior.
Without appropriate aerodynamic sampling, the extraordinary sensitivity of canine olfaction typically is not achieved. Current research seeks to understand the aerodynamics of the olfaction process through a series of flow visualization experiments as well as modeling efforts. Flow visualization is used to understand the aerodynamics of the canine nostril. Light-scattering techniques using Schlieren optics have been used to monitor the movement of airborne particles during olfaction.
Oro-nasal respiration of a subject can be monitored by measuring nasal pressure using an electrical pressure transducer. For example, a pair of nasal prongs can be provided, suitable for insertion into the lower portion of the subject's nares, and joining together via a small plenum chamber to form a single tube conveying the nasal pressure towards an electrical pressure transducer. Another prong is held in proximity with the subject's mouth. A baffle element extends downwards from a location above the open end of the prong to redirect a portion of oral airflow. The oral tube extends towards the electrical pressure transducers and conjoins with the nasal tube at a junction to form a common tube connected to the pressure transducer. The relative lengths and/or diameters of the nasal tube and the oral tube are arranged so that the respective pneumatic impedances are different, so that the contributions of respiratory airflow from each of said tubes are substantially equal.
Respiration may also be monitored by thermocouples. A sensor set is used with a monitor to monitor the respiration of a subject. In one arrangement, the sensor set includes a pair of spaced-apart parallel nasal thermocouple junctions, and an oral thermocouple junction aligned with one of the nasal thermocouple junctions. These junctions are supported by a support structure and are coupled to the monitor by a lead set and connector set. The sensor set is easily positioned on the subject's upper lip by looping the lead wires over the subject's ears and securing them underneath the subject's chin. The subject's respiration produces a temperature differential between the thermocouple junctions and a cold or reference junction, producing an output that is sensed by a monitor to indicate respiration. An alternative configuration employs thermistors as the sensor elements.
Known monitoring systems, however, have not proven fully adequate in the measurement and study of olfactory airflow. Thus, it can be seen that needs exist for improved testing devices and methods for analysis and measurement of airflow in and around the nasal cavities of animals and man. It is to the provision of improved testing devices and methods meeting these and other needs that the present invention is primarily directed.